# Applescript to change file extensions

I'm new at scripting, but I thought it would be handy to have a script that would change the extensions of selected files in Finder. I run this script from an automator service so that batch changing extensions in Finder is always just a right click away.

So far, it has worked as I expect, but since this is one of my first scripts, my question is: is there a cleaner way to obtain this functionality? Can anyone point out a case I haven't thought of in which this would fail?

What this script does:

• Asks the user for a new extension.
• Adds the new extension to any files that don't already have one.
• Changes the extension in other files even if it's a hidden file or has multiple points.

A test case that does not function correctly:

• The selected file's name has multiple points, but no extension. Here, my script replaces the text after the last point with the new extension.

Here's the code:

# Ask user for new extension to be used
set newExt to the text returned of (display dialog "Enter extension:" default answer "Do not include first point")

tell application "Finder"

# Make a list of the selected files in Finder
set selFiles to selection as list

set TID to AppleScript's text item delimiters

repeat with eachFile in selFiles

# Make a text item list of the file name delimited by points
set filePath to eachFile as text
set AppleScript's text item delimiters to {":"}
set fileName to last text item of filePath
set AppleScript's text item delimiters to {"."}
set textItems to text items of fileName

# Handle case where there is currently no extension, but one should be added.
if number of textItems is 1 then
set name of eachFile to fileName & "." & newExt

# If an extension does already exist...
else

set newName to ""
set numItems to number of items in textItems
set n to 1

repeat numItems times

# If the current text item is not the extension, add it & "." to the new file name.  No need here to consider the last text item since it's the old extension and we want to get rid of it.
if n is not numItems then
set newName to newName & item n in textItems & "."
set n to n + 1
end if

end repeat

set name of eachFile to newName & newExt

end if

end repeat

# Is this line necessary?  I just saw it at the end of someone else's script that had earlier set TID to AppleScript's text item delimiters.
set AppleScript's text item delimiters to TID

end tell


Feel free to use this if it would be useful for you.

• I have rolled back Rev 3 to 2. Please explain your improvement by posting an answer to your own question. Feb 4 '16 at 19:25
• Thanks 200_success. I posted the updated script as an answer. I suppose it's easier to follow the evolution of the script this way? Feb 5 '16 at 11:13

Breaking file paths into file names and file extensions is unneeded when properties exist to access these elements directly, in this case the name extension property.

set newExt to the text returned of (display dialog "Enter extension:" default answer "Do not include first point")

tell application "Finder"
set selFiles to selection
repeat with eachFile in selFiles
set name extension of eachFile to newExt
end repeat
end tell

• Much simpler, and I was not aware of the extension property, so thank you for that. However, this does not replace unusual extensions that are not recognized by the system. Feb 5 '16 at 11:12
• I can confirm that, I was trying to change a .yaml extension to .txt and was throwing a stack overflow error. Log the name extension of the file to see what the system thought it was dealing with and received this error: Can’t get name extension of alias \"Macintosh HD:Users:xxxxxxxx:Desktop:prebidServerBidders:client.yaml Nov 19 '20 at 14:39

I updated the script to handle the failed test case (sort of, at the users discretion). Previously, when I ran it on file names with multiple points and no pre-existing extension, text in the filename following the last point would be lost. As a workaround, I added a button to the dialog that forces the new extension to be appended to the full filename. This mode could be useful if you want to keep a record of the previous extension in the filename as well.

Updated code:

# Ask user for new extension to be used
set dRecord to (display dialog "Enter extension:" default answer "Do not include first extension point" buttons {"Cancel", "Force Appendation", "OK"} default button "OK" cancel button "Cancel")

set newExt to text returned of dRecord
set dButton to button returned of dRecord

# To change the extension in the default manner
if dButton = "OK" then

tell application "Finder"

# Make a list of the selected files in Finder
set selFiles to selection as list

set TID to AppleScript's text item delimiters

repeat with eachFile in selFiles

# Make a text item list of the file name delimited by points
set filePath to eachFile as text
set AppleScript's text item delimiters to {":"}
set fileName to last text item of filePath
set AppleScript's text item delimiters to {"."}
set textItems to text items of fileName

# Handle case where there is currently no extension, but one should be added.
if number of textItems is 1 then
set name of eachFile to fileName & "." & newExt

# If an extension does already exist...
else

set newName to ""
set numItems to number of items in textItems
set n to 1

repeat numItems times

# If the current text item is not the extension, add it & "." to the new file name.  No need here to consider the last text item since it's the old extension and we want to get rid of it.
if n is not numItems then
set newName to newName & item n in textItems & "."
set n to n + 1
end if

end repeat

set name of eachFile to newName & newExt

end if

end repeat

# Is this line necessary?  I just saw it at the end of someone else's script that had earlier set TID to AppleScript's text item delimiters.
set AppleScript's text item delimiters to TID

end tell

# To strictly append the new extension to the current filename
else if dButton = "Force Appendation" then

tell application "Finder"

# Make a list of the selected files in Finder
set selFiles to selection as list

repeat with eachFile in selFiles

set eachName to name of eachFile as text

set name of eachFile to eachName & "." & newExt

end repeat

end tell

end if